No one lives forever – nor do they last forever. At least not without a lot of tuneups.

As much as it may seem like the bodies of famous world leaders such as Vladimir Ilyich Lenin and Mao Zedong have been preserved for all eternity, their enduring physical presence is simply an illusion aided by science.

Only the Venezuelan officials who have promised to preserve Hugo Chavez and display his body “for eternity” inside a glass tomb know exactly how they’re going to do it.

But if they were to follow procedures that are used in the United States, the technique might be rather simple: repeat embalming.

“The first thing to remember about embalming as we do it in the U.S. is that it is designed to delay the natural deterioration of the body; it’s not forever,” said Vernie Fountain, a licensed embalmer and owner and founder of the Fountain National Academy of Professional Embalming Skills in Springfield, Missouri.

So what does that mean exactly? You might want to put down your sandwich before you read on.

In the U.S., most embalmers use a machine that injects fluid laced with chemicals, principally formaldehyde, into an artery of the body, while the majority of the blood is emptied from a vein. Often a chemical known as a humectant is added, which “helps to fill out the body, some of the hollow spaces, and adds a degree of moisture,” Fountain said.

While he stressed that he has no personal knowledge about the condition of Chavez’s body at the time of his death or when it was or will be embalmed, Fountain said one possible method of preserving his corpse is to follow the embalming process with a periodic injection of humectant or something similar to keep moisture in the tissues. Makeup also helps to cover areas that have gone brown with dehydration.

Just to be safe, Venezuelan officials could take an extra precautionary step and make a face mask, using Chavez’s real face to form a mold that could be placed over the flesh in the future “and keep it looking more like he did when he died,” Fountain said.

The process of embalming a body for a few days or many years is essentially the same, note Fountain and Camilo Jaramillo, a Colombian embalmer and alumnus of the American Academy McAllister Institute of Funeral Service.

“The difference when one wants to preserve a body for a long time is that the doctors apply more-concentrated amounts of the chemicals,” Jaramillo said. “It is a much slower process and must be done very carefully. … Indefinite preservation really doesn’t exist. … It requires periodic maintenance. … But no embalming stops decomposition; it only slows it,” he said.

The time it takes a body to deteriorate varies on the health and weight of the deceased and other environmental factors, including whether the body was refrigerated immediately after death. Regardless, the key is to embalm as soon as possible after death.

Ideally, a body would be embalmed “the very day or next morning, rather than three or five or six days down the road,” Fountain said. “But it’s not impossible. I have embalmed bodies that have been refrigerated for six months.”

Confronted with such a never-ending and unsavory task, why do countries such as Russia, China, Vietnam, and now Venezuela, go to such lengths to preserve their leaders’ remains?

“The decision to embalm Chavez is an attempt to include him in a pantheon of communist deities,” said Nina Tumarkin, a professor of history at Wellesley College and the author of “Lenin Lives! The Lenin Cult in Soviet Russia.”

“It’s a throwback to Soviet, communist times, and it might seem obsolete, but it might be the only pantheon where he belongs. Better to belong to the wrong club than none at all.”

Other socialist or communist leaders embalmed after dying include Russian dictator Josef Stalin, though his body was later removed, and North Korea’s father-and-son leaders Kim Il Sung and Kim Jong Il. But it was the famous display of Soviet founder Lenin in Moscow’s Red Square in 1924 that inspired the custom among left-leaning leaders.

And then there was Evita, the actress who married then-President Juan Domingo Peron and went on to claim a following of millions for her role in securing labor benefits for the working class, founding hospitals and helping women get the vote.

When she died young from uterine cancer in 1952, the military leaders who overthrew her husband in 1955 were so worried about a death cult that they took desperate measures to hide the body.

For two decades, the corpse was secretly moved around Argentina and then buried in an unmarked grave in Italy. Meanwhile several wax and fiberglass decoy corpses were sent out around the world. The real corpse remained in Rome until it was delivered to Peron’s home in 1971 while he was in exile in Spain.

Now it rests in her family’s crypt in the opulent Recoleta cemetery, a major tourist spot.

Lenin’s embalming process, still seen to this day as one of the finest examples of its kind, was presented to the world as a feat for Soviet science in its quest to preserve a body in such perfection.

But the idea was probably forced upon government officials, who may have feared another bloody revolution after they saw the huge crowds that showed up to say goodbye to Lenin.

Well over 500,000 people braved the biting winter cold just to catch a glimpse of the body.

Permanently staving off decomposition is no easy job.

When Chinese communist leader Mao Zedong died in 1976, the Chinese medical specialists tasked with preserving his corpse for permanent display were at a loss. In the middle of a rift with the Soviet Union, they couldn’t ask the Russians for the formula used on Lenin, according to a memoir by Mao’s doctor. Vietnam, which had embalmed Ho Chi Minh, rebuffed them, too, the doctor wrote.

In the end, the Chinese doctors used a formula found in a Western journal in a medical library in Beijing. They added extra doses of formaldehyde to boost the preservative effect.

“The results were shocking. Mao’s face was round as a ball, and his neck was now the width of his head,” Li Zhisui wrote in “The Private Life of Chairman Mao,” published outside China 18 years after Mao’s death.

The team managed to restore Mao to a more normal appearance with hours of careful massage and makeup, he said, but, just in case, a wax copy of the body was readied as a stand-in.